Simplify the following expression: $a = \dfrac{5}{4r} \div \dfrac{2}{10r}$
Answer: Dividing by an expression is the same as multiplying by its inverse. $a = \dfrac{5}{4r} \times \dfrac{10r}{2}$ When multiplying fractions, we multiply the numerators and the denominators. $a = \dfrac{ 5 \times 10r } { 4r \times 2}$ $a = \dfrac{50r}{8r}$ Simplify: $a = \dfrac{25}{4}$